I have Rega P25. It has hand-adjustable pots on the motor for removing resonance.

Uhh... how do I know if I have resonance?? And does one adjust it? The reason I ask: I feel the sound of my P25 should be deeper, more powerful sounding. It's a bit light.

Note: I live in the United States (if this matters) and I can follow instructions but I am not an electrical, or any other, engineer.

Thanks for any help,
Hukk

markinuk

16th November 2008 12:42 PM

Hi there,

I don't think adjusting these pots would be a good idea. Rega make these adjustments at the factory to minimize vibration from the motor. They probably use equipment to measure this, and certainly have the experience to do it so, unless there's something obviously wrong, DIY "fiddling" is likely to worsen performance.

Vibration from the motor would probably manifest itself in the form of background noise. I think the sound balance you describe is more likely to improve if you experiment with the surface on which the deck sits.

For example, if you are not using a wall-mounted shelf, try that if it is domestically acceptable, as it's what Rega recommend. There are plenty of DIY "recipes", too, for platforms and stands that have been found to work well with Rega decks.

You don't mention the cartridge you are using, and this can have an enormous effect on the sound the deck produces. A different model with stronger low frequencies might add weight to the sound.

HTH,

Mark

hukkfinn

16th November 2008 04:04 PM

Thanks for your reply.

My understanding is that these pots are user adjustable precisely so that home users can adjust, because the motor may be affected by the unique characteristics of an individual user's AC power.

That being said, I do not hear any hum or noise. So you're probably right, I don't need to touch them! If anybody thinks they might improve my sound quality, and clean up the bit of "grey" that this table produces, I'd be interested.

I use a Dynavector 20xL, famous for great bass slam. I have my P25 on a wall shelf using a Neuance platform -- about as good as it gets for any Rega.

"With this design, our skilled production technicians can "trim" the vibrations from the motor."

Both the fact that the instructions do not tell you how to adjust the motor and Rega's reference to 'our skilled technicians' implies to me that this is not an adjustment that they intend the user to make.

hukkfinn

16th November 2008 05:00 PM

That certainly suggests that users should not adjust! I looked and could not find those words on the Rega website. The P3-24 manual states, "High performance motor - The P3 - 24 uses the same very high quality low vibration motor, which is used in the P5 & 9 turntables. The clever controlling circuitry can be adjusted for phase angle of the motor coils resulting in very low vibration levels from the complete motor assembly."

That language leaves it unclear who might be doing the adjusting. However, it does not suggest that adjustment depends on your individual AC power, so again it suggests that the factory does this, once.

Thanks for your help.
Hukk

sq225917

19th November 2008 01:12 PM

If you have a DV cart on your arm then it definitely needs some adjustment making for the increased height of the cartridge body.

So if you have not already raised the back of the tonearm, then you need to do this to compensate for the extra height at the front of the arm, which effectively tilts the cart and stylus back.

You need to raise the back of the arm between 2-4mm, the sweet spot will be somewhere in the middle.

There are various VTA adjustment devices available on 'the Bay' to allow you to do this from steel washers that go under your arm to teflon filled CNC machined adjusters from guys like Peter Riggle

Dialing the correct arm heigth and VTA in will allow you bass to snap back into focus, giving you the slam you are missing.

(Rega p5 and Dv20x owner).

federico moreno

19th November 2008 03:24 PM

...if you´re bold...

...and fearless, you can use an stethoscope to check out for mechanical noise in a turntable; then, you can experiment finding the more desirable settings in the motor. Be careful.

I don´t know the Rega p25, but analogue stuff are meant to be tweaked. But, again, be careful, and take note of the original position of the settings...

;)
I have done this kind of things in the past to optimize residual noise issues on Thorens TD125, Barthe Rotofluid and in my own diy TT. With good results, of course.

A somewhat barbaric, but very useful method to evaluate residual noise -assuming that you have a MM cart- : put there an old stylus, and very carefully lay the tonearm/cart/stylus on the plinth.
If you can´t do so for clearance issues, you can use some kind of ¨bridge¨ to transfer the noise from the plinth to the stylus, ie: a rigid bar of wood .The cart is and ad-hoc transducer able transform the mechanical energy in sound, so you now will be able to ¨hear¨ the residual noise of your TT via a pair of headphones... :devilr:
There are various sources of noise in a TT, so you can do fancy experiments.

Don´t dismiss Markinuk advice about carts, or the VTA issue.
And try different type of mats too: glass, rubber, cork, even paper and dots...

Have fun!

federico moreno

19th November 2008 03:44 PM

glass mat

I have noticed that the Rega p25 has a glass platter, so my recomendation of a glass mat is out of the question..:xeye:

When using glass mats in my TT´s -5mm float- the sound takes a somewhat clinical edge: detailed, good mids, but a dry bass.

Definitely, you should try some cork, or at least a bunch of rubber or cork dots strategically placed in the platter (they´re removable, so don´t worry)

Cheers

hukkfinn

19th November 2008 04:31 PM

Thanks for your reply. I have a 2mm spacer in place and also tried the 4mm spacer. I agree that 3mm would be ideal (good ear!). I'm just looking for anybody who has adjusted their motor. So far, it sounds like the consensus is that this is a factory adjustment, and should not be customized for the owner's particular AC characteristics. I am surprised that nobody here has dug into this adjustment! (Mainly because you guys are light years ahead of me in tweaking every other element of this and other turntables). This forum is not alone -- nobody on Vinyl Asylum has indicated that they have fooled with it either.
Hukk

sq225917

19th November 2008 05:14 PM

When investigating sources of noise in my P5, which is effectively a p25 with extruded alloy surround and a slightly updated Rb700 arm, i looked at adjusting the motor via the trim pots. In the end i found that cutting through the melamine where the motor is mounted and replacing the melamine with a layer of carbon-ply-carbon sheet had the desired effect, a huge drop in motor noise transmitted through the deck to the stylus.

In the end i did the same thing for the arm, before transplanting all the component parts to a wooden butchers block and then lifting the bearing magnetically. Now it's a whole other machine.